Investigation of compressive strength and microstructures of activated cement free binder from fly ash - calcium carbide residue mixture

This paper investigates compressive strength and microstructural properties of activated cement free binder from fly ash (FA) - calcium carbide residue (CC). Different activation methods to enhance the strength of the FA-CC mixture were used including the following: 1) curing at elevated temperature of 60 °C, 2) adding 1% NaOH by weight of binder and 3) combining both 1% NaOH by weight of binder and curing at temperature of 60 °C. The compressive strengths of mortars with different activation techniques were determined at 3, 7, 28, and 90 days. Microstructural properties of activated cement free binder from the FA-CC mixture, that is, XRD patterns, SEM microscopy, EDS analysis, and degree of reaction were examined. Results from this study revealed that the activated cement free binder from FA-CC had components of Ca, Al, and Si and indicated CSH and CASH likewise the end products of pozzolanic reaction. Use of activation techniques had significantly affected on the microstructure in cementing system. The activated cement free binder from FA-CC mixture with addition of 1% NaOH and curing at 60 °C increased binder strength and promoted the formation of CSH, CASH, and some amount of NASH phase or hybrid C(N)ASH.